1,721,109 research outputs found
Analysis of Capillary Flow Driven Model for Water Transport in PEFC Cathode Catalyst Layer: Consideration of Mixed Wettability and Pore Size Distribution
No full textThe solid matrix of the porous cathode catalyst layer (CCL) of a polymer electrolyte fuel cell
is made of two different materials (carbon with supported Pt and ionomer), which are
characterized by different wettability (i.e. contact angles). This paper discusses the need for
considering the combined consideration of the mixed wettability and the distributed pore
structure of CCL in modelling the transport of liquid water and oxygen gas. A simple 1-D
model that considers two different pore size distributions, derived from experimental
capillary pressureesaturation literature data, for the hydrophobic and hydrophilic pores is
presented. The results indicate that for water to be transported in liquid-state through the
CCL, the liquid saturation is such that only very small hydrophobic pores remain available
for gas transport such that Knudsen diffusion will dominate and must be considered in CCL
models
FCpowered RBS: Data Analysis and System Optimization
No full textThe previous works on the use of PEM Fuel Cell based power supply system for the operation of off-grid RBS (Radio Base Stations) sites showed a strong influence of system design parameters on the energy conversion performance. In this paper a perturbation of system design is performed through validated models to understand better the variability of performance over a full year operation. Results show that a ratio of energy produced by fossil over energy produced by renewables sources of 0.2 can be reached slightly increasing the photovoltaic plant size without affecting drastically the renewable exploitation. Moreover a positive Net Present Value can be achieved in comparison with the traditional diesel genset solution (from 260k(sic) to 350k(sic)). The NPV value increases with the PV size and with a reduction of the battery size that leads to a steep reduction in the RES exploitation. Therefore, an optimum has to be sought as a compromise between the two aspects. (C) 2019 The Authors. Published by Elsevier Ltd
Experimental–numerical analysis of a biomass fueled microgeneration power-plant based on microturbine
No full textThermal use of biomass may have a significant role in the scheme of distributed power generation from renewable sources as it is intrinsically programmable. Moreover, if the furnace is designed for flexible fueling (multifueling), this feature gives maximum flexibility also from the standpoint of fuel availability and storage over the year. To fully exploit the fuel potential, the optimal size for these systems is in the lower range end (100 kW) for reasons mainly related to the fuel logistic chain. A Combined Heat and Power (CHP) configuration is furthermore important to balance the relatively low electric efficiency (in the order of 15% and less). In this paper a technology based on an Externally Fired Gas Turbine (EFGT) fed by woody biomass is demonstrated in the range of 70 kW electric power output. A multifuel prototype power-plant realized at the University of Rome Tor Vergata is described, and experimental data in terms of power, efficiency and fuel consumption are presented. To better understand the impact of fuel properties on power-plant performance, a model has also been developed, by means of physical submodels describing each component of the power-plant (biomass furnace, heat exchangers, compressor and turbine). The use of simple economic and management models is also discussed to better assess the economic sustainability of the solution depending on the characteristics of the fuel (fuel-end), matched with the utilization pattern (user-end), with special regard to thermal energy value over the year
Heat and Mass Transfer Evaluation in the Channels of an Automotive Catalytic Converter by Detailed Fluid-Dynamic and Chemical Simulation
No full textThe role of numerical simulation to drive the catalytic converter development becomes more important as more efficient spark ignition engines after-treatment devices are required. The use of simplified approaches using rather simple correlations for heat and mass transfer in a channel has been widely used to obtain computational simplicity and sufficient accuracy. However, these approaches always require specific experimental tuning so reducing their predictive capabilities. The feasibility of a computational fluid dynamics three-dimensional (3D) model coupled to a surface chemistry solver is evaluated in this paper as a tool to increase model predictivity then allowing the detailed study of the performance of a catalytic converter under widely varying operating conditions. The model is based on FLUENT to solve the steady-state 3D transport of mass, momentum and energy for a gas mixture channel flow, and it is coupled to a powerful surface chemistry tool (CANTERA). Checked with respect to literature available experimental data, this approach has proved its predictive capabilities not requiring an ad hoc tuning of the parameter set. Heat and mass transfer characteristics of channels with different section shapes (sinusoidal, hexagonal, and squared) have then been analyzed. Results mainly indicate that a significant influence of operating temperature can be observed on Nusselt and Sherwood profiles and that traditional correlations, as well as the use of heat/mass transfer analogy, may give remarkable errors (up to 30% along one-third of the whole channel during light-off conditions) in the evaluation of the converter performance. The proposed approach represents an appropriate tool to generate local heat and mass transfer correlations for less accurate, but more comprehensive, 1D models, either directly during the calculation or off-line, to build a proper data base
CFD-Based design of micro-tubular solid oxide fuel cells
No full textMicrotubular solid oxide fuel cells (MT-SOFCs) are interesting for portable and auxiliary power units energy production systems, due to their extremely fast startup time. However, a single cell provides power in the range of 1 W, thus the number of microtubes to reach a kW scale is relevant and packaging design issues arise also. In this paper a specifically developed design procedure is presented to face with system issues and bringing into account fluid-dynamic and thermal influence on system performance. The procedure also simplifies the stack manifold design by means of a modular scale-up procedure starting from a basic optimized configuration. To this aim, a computational fluid dynamics (CFD) model has been integrated with specific models for fuel cell simulation and then validated with tailored experimental data by varying operating conditions in terms of fuel utilization and electric load. A comprehensive three–dimensional (3D) thermal-fluid-dynamic model has then been applied to the analysis of both micro-assembly (i.e., 15 tube assembly) and midi-assembly (up to 45 tubes), showing an important role of local phenomena as current homogeneity and reactant local concentration that have a strong influence on power density and temperature distribution. Microreactor power density in the range of 0.3 kW/l have been demonstrated and a specific manifold design has been realized paving the way toward a modular realization of a 1 kW MT-SOF
3D effects of water-saturation distribution on polymeric electrolyte fuel cell (PEFC) performance
No full textWater management in cathode gas diffusion layers and catalyst layers of PEFCs (Polymer
Electrolyte Fuel Cells) plays an important role toward the obtainment of optimal performance.
Flooding may indeed occur under different operating conditions, in these
components, requiring special attention both in the development and in the design
processes. Simulation is a reliable tool to support the design of PEFCs, and thus provide
designers with a better interpretation of experimental data. Flooding within porous media
is still a critical issue for multiphase flow fuel cell modeling, representing a challenge in
terms of model reliability.
This paper aims at extending the validity of a literature available 1D GDL multiphase model
presented in Ref. [24]. Special attention has been devoted to the analysis of the difference
between multiphase and non-multiphase (multispecies) approaches, and to the 3D aspects
of cell design related to flooding issues. Results indicate that flooding must be treated as
a 3D phenomenon, as it has a different impact on the different active area regions. In fact,
although the land is the most affected zone, current is mainly limited in the channel zone
close to the gas inlet section
Domestic distributed power generation: Effect of sizing and energy management strategy on the environmental efficiency of a photovoltaic-battery-fuel cell system
No full textThe maximum exploitation of local renewable energy sources is a key feature of DG (Distributed Generation) systems: to this aim, HPSs (Hybrid Power Systems), integrating renewable and non-renewable power sources with local energy storage may represent an effective solution, although they may require an optimum utilization of the different sub-systems, for example if including FCs (Fuel Cells).
This work introduces a new definition of system efficiency, which is linked to a class index defined according to the local renewable energy availability. The system efficiency is also demonstrated as a function of two performance parameters describing the effectiveness, respectively, of renewable and fossil energy conversion. The new set of parameters is used to study an experimental DG hybrid system including photovoltaic panels and FCs, representing a detached house. A test facility has been used to validate numerical models. A full year period was then simulated, to single out that the new set of parameters could help evaluate the HPS environmental performance and the effective renewable energy exploitation; the class index also helps evaluating the real system efficiency and environmental performance, which strongly depends on the local renewable energy available. An optimal management strategy is also found respect to the FCs utilization
Studio dell’efficienza di filtrazione nel numero e nella massa di un filtro per particolato close-coupled
No full textBiomass energy conversion in EFGT (Externally Fired Gas Turbine): An experimental-numerical analysis
No full textBiomass pyrolysis modeling of systems at laboratory scale with experimental validation
No full textPurpose – Thermochemical conversion processes are one of the possible solutions for the flexible production of electric and thermal power from biomass. The pyrolysis degradation process presents, among the others, the interesting features of biofuels and high energy density bio-oil production potential high conversion rate. In this paper, numerical results of a slow batch and continuous fast pyrolyzers, are presented, aiming at validating both a tridimensional computational fluid dynamics-discrete element method (CFD–DEM) and a monodimensional distributed activation energy model (DAEM) represents with data collected in dedicated experiments. The purpose of this paper is then to provide reliable models for industrial scale-up and direct design purposes. Design/methodology/approach – The slow pyrolysis experimental system, a batch of small-scale constant-pressure bomb for allothermic conversion processes, is presented. A DEM numerical model has been implemented by means of a modified OpenFOAM solver. The fast pyrolysis experimental system and a lab scale screw reactor designed for biomass fast pyrolysis conversion are also presented along with a 1D numerical model to represent its operation. The model which is developed for continuous stationary feeding conditions and based on a four-parallel reaction chemical framework is presented in detail. Findings – The slow pyrolysis numerical results are compared with experimental data in terms of both gaseous species production and reduction of the bed height showing good predictive capabilities. Fast pyrolysis numerical results have been compared to the experimental data obtained from the fast pyrolysis process of spruce wood pellet. The comparison shows that the chemical reaction modeling based on a Gaussian DAEM is capable of giving results in very good agreement with the bio-oil yield evaluated experimentally. Originality/value – As general results of the proposed activities, a mixed experimental and numerical approach has demonstrated a very good potential in developing design tools for pyrolysis development
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